bug(nodeunschedulable): register missing Pod event for NodeUnschedulable plugin

pkg/scheduler/framework/plugins/nodeunschedulable/node_unschedulable.go

@@ -51,12 +51,56 @@ const (
 // EventsToRegister returns the possible events that may make a Pod
 // failed by this plugin schedulable.
 func (pl *NodeUnschedulable) EventsToRegister(_ context.Context) ([]framework.ClusterEventWithHint, error) {
-	// preCheck is not used when QHint is enabled.
+	if !pl.enableSchedulingQueueHint {
+		return []framework.ClusterEventWithHint{
+			// A note about UpdateNodeLabel event:
+			// Ideally, it's supposed to register only Add | UpdateNodeTaint because UpdateNodeLabel will never change the result from this plugin.
+			// But, we may miss Node/Add event due to preCheck, and we decided to register UpdateNodeTaint | UpdateNodeLabel for all plugins registering Node/Add.
+			// See: https://github.com/kubernetes/kubernetes/issues/109437
+			{Event: framework.ClusterEvent{Resource: framework.Node, ActionType: framework.Add | framework.UpdateNodeTaint | framework.UpdateNodeLabel}, QueueingHintFn: pl.isSchedulableAfterNodeChange},
+		}, nil
+	}
+
 	return []framework.ClusterEventWithHint{
+		// When QueueingHint is enabled, we don't use preCheck and we don't need to register UpdateNodeLabel event.
 		{Event: framework.ClusterEvent{Resource: framework.Node, ActionType: framework.Add | framework.UpdateNodeTaint}, QueueingHintFn: pl.isSchedulableAfterNodeChange},
+		// When the QueueingHint feature is enabled,
+		// the scheduling queue uses Pod/Update Queueing Hint
+		// to determine whether a Pod's update makes the Pod schedulable or not.
+		// https://github.com/kubernetes/kubernetes/pull/122234
+		{Event: framework.ClusterEvent{Resource: framework.Pod, ActionType: framework.UpdatePodTolerations}, QueueingHintFn: pl.isSchedulableAfterPodTolerationChange},
 	}, nil
 }
 
+// isSchedulableAfterPodTolerationChange is invoked whenever a pod's toleration changed.
+func (pl *NodeUnschedulable) isSchedulableAfterPodTolerationChange(logger klog.Logger, pod *v1.Pod, oldObj, newObj interface{}) (framework.QueueingHint, error) {
+	_, modifiedPod, err := util.As[*v1.Pod](oldObj, newObj)
+	if err != nil {
+		return framework.Queue, err
+	}
+
+	if pod.UID == modifiedPod.UID {
+		// Note: we don't need to check oldPod tolerations the taint because:
+		// - Taint can be added, but can't be modified nor removed.
+		// - If the Pod already has the toleration, it shouldn't have rejected by this plugin in the first place.
+		//   Meaning, here this Pod has been rejected by this plugin, and hence it shouldn't have the toleration yet.
+		if v1helper.TolerationsTolerateTaint(modifiedPod.Spec.Tolerations, &v1.Taint{
+			Key:    v1.TaintNodeUnschedulable,
+			Effect: v1.TaintEffectNoSchedule,
+		}) {
+			// This update makes the pod tolerate the unschedulable taint.
+			logger.V(5).Info("a new toleration is added for the unschedulable Pod, and it may make it schedulable", "pod", klog.KObj(modifiedPod))
+			return framework.Queue, nil
+		}
+		logger.V(5).Info("a new toleration is added for the unschedulable Pod, but it's an unrelated toleration", "pod", klog.KObj(modifiedPod))
+		return framework.QueueSkip, nil
+	}
+
+	logger.V(5).Info("a new toleration is added for a Pod, but it's an unrelated Pod and wouldn't change the TaintToleration plugin's decision", "pod", klog.KObj(modifiedPod))
+
+	return framework.QueueSkip, nil
+}
+
 // isSchedulableAfterNodeChange is invoked for all node events reported by
 // an informer. It checks whether that change made a previously unschedulable
 // pod schedulable.

pkg/scheduler/framework/plugins/nodeunschedulable/node_unschedulable_test.go

@@ -23,6 +23,7 @@ import (
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/kubernetes/pkg/scheduler/framework"
 	"k8s.io/kubernetes/pkg/scheduler/framework/plugins/feature"
+	st "k8s.io/kubernetes/pkg/scheduler/testing"
 	"k8s.io/kubernetes/test/utils/ktesting"
 )
 
@@ -96,14 +97,14 @@ func TestIsSchedulableAfterNodeChange(t *testing.T) {
 		expectedErr    bool
 	}{
 		{
-			name:         "backoff-wrong-new-object",
+			name:         "error-wrong-new-object",
 			pod:          &v1.Pod{},
 			newObj:       "not-a-node",
 			expectedHint: framework.Queue,
 			expectedErr:  true,
 		},
 		{
-			name: "backoff-wrong-old-object",
+			name: "error-wrong-old-object",
 			pod:  &v1.Pod{},
 			newObj: &v1.Node{
 				Spec: v1.NodeSpec{
@@ -186,3 +187,64 @@ func TestIsSchedulableAfterNodeChange(t *testing.T) {
 		})
 	}
 }
+
+func TestIsSchedulableAfterPodTolerationChange(t *testing.T) {
+	testCases := []struct {
+		name           string
+		pod            *v1.Pod
+		oldObj, newObj interface{}
+		expectedHint   framework.QueueingHint
+		expectedErr    bool
+	}{
+		{
+			name:         "error-wrong-new-object",
+			pod:          &v1.Pod{},
+			newObj:       "not-a-pod",
+			expectedHint: framework.Queue,
+			expectedErr:  true,
+		},
+		{
+			name:         "error-wrong-old-object",
+			pod:          &v1.Pod{},
+			newObj:       &v1.Pod{},
+			oldObj:       "not-a-pod",
+			expectedHint: framework.Queue,
+			expectedErr:  true,
+		},
+		{
+			name:         "skip-different-pod-update",
+			pod:          st.MakePod().UID("uid").Obj(),
+			newObj:       st.MakePod().UID("different-uid").Toleration(v1.TaintNodeUnschedulable).Obj(),
+			oldObj:       st.MakePod().UID("different-uid").Obj(),
+			expectedHint: framework.QueueSkip,
+		},
+		{
+			name:         "queue-when-the-unsched-pod-gets-toleration",
+			pod:          st.MakePod().UID("uid").Obj(),
+			newObj:       st.MakePod().UID("uid").Toleration(v1.TaintNodeUnschedulable).Obj(),
+			oldObj:       st.MakePod().UID("uid").Obj(),
+			expectedHint: framework.Queue,
+		},
+		{
+			name:         "skip-when-the-unsched-pod-gets-unrelated-toleration",
+			pod:          st.MakePod().UID("uid").Obj(),
+			newObj:       st.MakePod().UID("uid").Toleration("unrelated-key").Obj(),
+			oldObj:       st.MakePod().UID("uid").Obj(),
+			expectedHint: framework.QueueSkip,
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			logger, _ := ktesting.NewTestContext(t)
+			pl := &NodeUnschedulable{}
+			got, err := pl.isSchedulableAfterPodTolerationChange(logger, testCase.pod, testCase.oldObj, testCase.newObj)
+			if err != nil && !testCase.expectedErr {
+				t.Errorf("unexpected error: %v", err)
+			}
+			if got != testCase.expectedHint {
+				t.Errorf("isSchedulableAfterNodeChange() = %v, want %v", got, testCase.expectedHint)
+			}
+		})
+	}
+}

pkg/scheduler/framework/types.go

@@ -69,7 +69,8 @@ const (
 	UpdatePodLabel
 	// UpdatePodScaleDown is an update for pod's scale down (i.e., any resource request is reduced).
 	UpdatePodScaleDown
-	// UpdatePodTolerations is an update for pod's tolerations.
+	// UpdatePodTolerations is an addition for pod's tolerations.
+	// (Due to API validation, we can add, but cannot modify or remove tolerations.)
 	UpdatePodTolerations
 	// UpdatePodSchedulingGatesEliminated is an update for pod's scheduling gates, which eliminates all scheduling gates in the Pod.
 	UpdatePodSchedulingGatesEliminated